Degenerative Myelopathy (DM)

Canine Degenerative Myelopathy (DM), is a heartbreaking progressive neurological disease affecting the spinal cord that mimics the symptoms of ALS (Amyotrophic lateral sclerosis) and/or PPMS (Primary-progressive multiple sclerosis). It is also known as Chronic Degenerative Radiculomyelopathy (CDRM), and Canine Degenerative Myelopathy. It is currently incurable and fatal.

The Spinal cord contains neurons (nerves) that carry messages between the brain and the rest of the body. The spinal cord is surrounded by a protective, insulating sheath of tissue, called Myelin. If a dog has DM, this Myelin Sheath starts to break down leaving the neurons exposed, which then become damaged and can die. This causes a loss of communication between the brain and the body and the messages to function do not get through. This damage starts with the dog losing the ability to use their rear legs, and will progress up through the core (middle of the dog) and then eventually reach the front legs, before finally affecting vital organs such as the respiratory system.

This process doesn't happen suddenly, it is a slow process that takes many months and in some cases even years (from first symptoms to End Stage, the time span can be as much as 3 years or so). How long a dog can survive with DM depends upon many factors.. the age of the dog at onset, the demeanor of the dog and of course the ability of the owner to be able to care for the dog through the DM journey, and that can depend on many factors including personal circumstances, family, work and finances.

RESEARCH ARTICLES

DNA TEST LABS

DM is an older dog disease with most signs starting to show around the average age of 8 years and older and there is no differentiation between male or female dogs both sexes are affected equally. It used to be thought of as a GSD or 'large dog' disease, but has now been found in many different breeds of dogs including: German Shepherd Dogs, Boxers, Pembroke Welsh Corgis, Chesapeake Bay Retrievers, Rhodesian Ridgebacks, Bernese Mountain Dogs, Wire Fox Terrier and others. In 2009, a mutation in the SOD1 gene was discovered to suggest the risk factor of DM, it is not however, a diagnosis of DM, but is a useful tool to use as part of the testing for ruling out the many other diseases or issues that can look like DM. This mutated gene has now been found in over 124 breeds.

What causes DM ?

The actual cause of this disease is still unknown, however the mutation in the SOD1 gene is a risk factor for developing Degenerative Myelopathy in many breeds, although this is not a diagnosis of DM. Mutations in SOD1 are also associated with familial Amyotrophic Lateral Sclerosis, ALS, (Lou Gehrig's disease) in people. Additional genes affecting onset of DM have since been found in: The Bernese Mountain dog, (a second mutation of the SOD1 gene often referred to as SOD1-B or exon 1) and another in the Pembroke Welsh Corgi, (a mutation found in the SP110 gene, known as a Modifier gene) this will determine the age of onset for DM. Though not yet clinically confirmed, it is thought GSD's may get a form of the disease very similar to Primary Progressive Multiple Sclerosis (PPMS). In the former DM Flash Test, an Alelle 1101J was implicated in DM of the German Shepherd Dog, a gene associated with PPMS in people.

Recent evidence suggests there are most likely, more additional genes or environmental factors determining the onset of DM in some breeds.

We have a lot more knowledge now than we did when DM was first recognised back in 1972 in GSD's, but sadly at this time there are still many unknowns about the causes of DM, whether they are additional genes or environmental issues, but it is clear more research is needed to uncover these 'unknowns' and to help us find treatments and finally a Cure.

At this time, there is sadly still no definitive test to confirm DM in a living dog. DM can only be a 'Confirmed Diagnosis' by having a necropsy (autopsy in humans) performed after a dog has passed. A series of tests, known as

'Rule Out Testing' are important to have carried out if possible, to rule out the many other diseases and conditions that can have the same or similar symptoms as DM. If nothing conclusive is found from this testing, you will be left with what is known as a 'Presumptive Diagnosis of Exclusion'.

Testing understandably though, is not always possible for some as it can be costly and will depend on the owners

financial, family and personal circumstances in conjunction with the age of the dog, however, we do recommend as much as is possible.

MAKE SURE your veterinarian, or a veterinary neurologist, examines your dog for these other conditions that may also involve the spine and/or cause similar symptoms as some are not terminal, can be cured or require different treatment to DM.

Recommended Tests to help rule out other conditions:

A full Neurological examination
DM DNA test;
Blood tests, to include Lyme disease testing;
X-Rays;
MRI, and CSF analysis

A 'diagnosis of DM' cannot be based on a single test alone........such as a physical examination, the way a dog is walking, flipping of the paw (also known as knuckling) an X-ray, blood work or a just a DNA test. To arrive at a 'Presumptive DM diagnosis', an examination by a board certified neurologist and an MRI is also needed. It is worth noting there is a difference between an Xray and MRI. Xrays produce flat images of the inside organs and bones of the body, is cheaper and quicker, but an MRI, although more costly, is able to take much more high resolution, clearer and detailed images than an Xray, particularly of soft tissue, tumors and most spinal issues.

How can I tell if my dog has DM ?

Remember...

Like most diseases, DM has a pattern of progression, there can be slight variations in...time scales, responses of the patient to symptoms (due to individual biological, emotional and physical make-up) and slight variations of some lessor symptoms, when or if they occur. However, these will not alter the established path of the disease.

DM has a slow onset and is NOT Painful in itself.

If any of the early symptoms listed below occur suddenly or if your dog is showing any signs of pain, you are most likely not dealing exclusively, or at all with DM.

DM does NOT come on suddenly.

Other disorders such as Disc disease, (IVDD), Disk herniation, Tumors and FCE (a stroke in the spinal cord) can also cause similar symptoms to DM, but with a much more rapid onset.

It is important to try to establish as far as is possible from the start if your dog 'may' have DM.

Some other diseases and conditions are not 'terminal', but can look like DM and have the same or similar symptoms. Some can be cured or require different treatment or therapy. For Example: DM dogs need exercise to help slow DM by maintaining muscle strength, whereby some conditions may require restricted exercise to prevent further damage.

Lots of Symptoms that look like DM, can be other diseases or issues.

Eg. Knuckling of the paws, dragging of the legs, dipping down in the back, difficulty getting up and even appearance of lack of pain can be caused by other issues that can mimic the symptoms of DM.

DM is extremely rare in a dog under 5 years of age.

If your dog is younger, it is extremely unlikely it is DM, but another condition or even another 'Myelopathy', but not DM, Which is also known as Canine Degenerative Radiculomyelopathy (CDRM).

Make sure you understand what your Veterinarian feels is the cause of the issues with your companion. If you are not sure, then asked them to clarify for you. Sometimes vets use the 'literal term' 'Degenerative Myelopathy', meaning 'Degenerative' = to deteriorate and get worse and 'Myelopathy' = disease or damage of the spinal cord. This term can refer to a wide variety of neurologic diseases in dogs, not just 'DM' as it is now known and can sometimes cause confusion.

CONDITIONS SIMILAR TO DM

STAGES OF DM - Progression

Stage 1 - VERY EARLY/EARLY STAGE

DM initially affects the back legs only, NOT the front legs.

At first you may notice rear limb weakness and slight muscle loss, difficulty transferring from lying down or sitting to standing, and/or an inability or reluctance to climb stairs, jump into the car, or onto furniture. This may be thought of as aging or Arthritis and can of course, often be a contributing factor. You may notice a scraping sound on the pavements/ sidewalks as the dog may drag one or both paws when walking and you notice when you check the paws the middle two nails are worn further than the others. At this point you will most likely have seen your veterinarian and DM could have been mentioned. Eventually the scraping can become 'knuckling' of the paws (walking on the tops of one or both paws - this is loss of conscious proprioception)

NOTE: The symptoms above can also be typical of other diseases such as Arthritis, Hip Dysplacia, Spinal issues such as IVDD and other conditions. MAKE SURE that your veterinarian, or a veterinary neurologist, examines your dog for other conditions that may also involve the spine.

Stage 2 - INTERMEDIATE STAGE

Worsening signs of weakness in the rear end of the dog.

As you enter Stage 2 Intermediate Stages, there will be a worsening of Stage 1 symptoms. The tail may become limp. There will be more crossing of the hind limbs, legs getting tangled as they walk like a 'drunken sailor'. They can get stuck as they turn as their legs won't go where they want them to. They will 'slink' down in their back end as their legs become unable to support their weight fully. Fecal and/or Urinary incontinence can occur. As they progress through the Intermediate stage, they can become anxious and vocalization can increase. Twitching of the rear limbs may become more 'violent' when laying down or even asleep, due to misfiring of the nerves. You may note a hoarseness in the bark and/or loss of volume. They will eventually become unable to stand up at all unaided using their back legs and will start pulling themselves around using their front legs, this is known as being 'Down in the Back'. Pressure sores can develop as they are unable to fully move around so much. UTI's can develop. They may start to have what appears to be weakness in the front legs, at this stage it is not usually progression of DM though, but 'compensation pain' as a result of additional stress from pulling themselves around by their front half and can mostly be managed by mild pain meds and massage.

NOTE: A dog with the right aids, support and care can manage for quite a long while at this stage, although as DM progresses, DM will speed up slightly and is quicker from Intermediate stage to End stage, than from Early stage to Intermediate stage .

Stage 3 - END/LATE STAGE

Movement of weakness through the core of the dogs body (middle section) to affect the front end and legs.

At this stage, progression can be more rapid, but can still plateau for quite a while. You will see floppiness in the core develop, and they will become unable to use their front legs or be able to sit up. There will be more muscle loss in the shoulder area as well as front legs and hind quarters. UTI's can become more difficult to overcome and pressure sores may be more persistent. They will progress to being unable to keep themselves in an upright position on their belly and will need assistance to do this. The nervous system's spinal cord and brain stem are the only structures actually affected by DM, however, weakness from DM can have secondary effects on the dog such as the pressure sores and systemic infections.

NOTE: A dog can pass naturally from End Stage DM, however vigilant monitoring and 24 hr care is essential at all times to ensure a crisis does not arise and there is no distress for the dog, in which case most owners would ensure euthanasia is carried out to prevent this happening.

Stage 4 - VERY END STAGE

Progression to Multi Organ Failure.

The disease will progress to the brain stem and eventually to the cranial nerves which may affect vital organs such as the diaphragm and breathing. There can eventually be kidney, lung and heart failure. Asphyxiation can occur. Death from DM, should it get to that stage results from multi organ failure.

NOTE: Very End Stage can be very distressing for both dog and owner. Most people who care for their dogs even through End Stage DM, monitor their dogs vigilantly and choose euthanasia as soon as changes occur to ensure a crisis situation of Very End Stage is not reached.

GENETICS

In 2009 a DM DNA test became available for a mutation of the SOD1 gene that has been associated in dogs with Degenerative Myelopathy. This is a blood test from your veterinarian or a saliva swab test you can send for and carry out yourself at home.

The test, first available through the U.S.based Orthopedic Foundation for Animals, is only recommended for predisposed breeds, but can be performed on DNA from any dog on samples collected through swabbing the inside of the animal's cheek with a sterile cotton swab or through venipuncture.

The DM DNA test is now available from many testing laboratories around the world including the UK, Europe, US and Canada.

ALSO REMEMBER ... The DM DNA test IS NOT A DIAGNOSIS OF DM, but a Risk Factor Indicator of possible DM. Recent evidence suggests there are additional genes or environmental causes of DM in some breeds, but this test is a non invasive/non expensive test along with other testing, to help 'Rule Out' other issues that can look like DM and find out what may be going on with your companion. It is also helpful for making informed Breeding decisions or when selecting a new puppy to purchase

DM DNA TEST RESULTS:

This is a helpful diagram for interpreting the results

(The term 'Affected' means Affected with 2 copies of the gene, it does not mean Affected with DM)

Sensible Breeding decisions can be calculated using this information:

If BOTH PARENTS ARE CLEAR (N/N) .... then all puppies will be clear
If ONE PARENT IS CLEAR (N/N) AND ONE PARENT IS A CARRIER (N/A).... roughly 50% will be clear (N/N) and 50% will be carriers (N/A)
IF BOTH PARENTS ARE CARRIERS (N/A).... roughly 25% will be clear (N/N), 50% will be carriers (N/A), and 25% will be affected (A/A)
IF ONE PARENT IS CLEAR (N/N) AND ONE PARENT IS AFFECTED (A/A).... all puppies will be carriers (N/A)